Electric synchronizing system



Aug, 30, 1932.

IIYPU T A. J. MADDOCK 1,874,774

ELECTRIC SYNCHRONIZING SYSTEI Filed June. 5, 1931 Inventor: A Ian J. Maddock,

H i s Attorneg.

Patented Aug. 30, 1932 UNITED STATES PATENT OFFICE ALAN JULIAN MADDOCK, OF WALLSEND-ON-TYNE, ENGLAND, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK ELECTRIC SYNCHRONIZING SYSTEM Application filed June 5, 1931, Serial No. 542,418, and in Great Britain June 5, 1930.

The present invention relates to the synchronizing of two rotating bodies located at diiierent points and associated with two separate apparatus which will be hereinafter termed the transmitter and the receiver respectively.

The invention relates particularly to electric synchronizing systems in which a transmitter sends out at periodic intervals elec- 19 tric impulses which are utilized at a receiver to effect synchronization of the rotating bodies at the transmitter and receiver,

The object of the invention is to provide a synchronizing system in which the energy utilized in driving synchronously the rotating body at the receiver is rendered entirely independent of the energy of the received impulses, and to this end the invention consists in the provision of a phonic Wheel or 20 like device for driving the rotating body above referred to and deriving its power from a local source of direct current supply, together with means for causing the direct current supply to be converted into driving 5 impulses which are synchronized with the impulses received from the transmitter.

The invention preferably involves the use of a gas-filled electric arc discharge device provided with means for controlling the. passage of an arc between a cathode and an anode of the type described, for example, in

United States application Serial No. 349,436.

Such a device has the characteristic that a negative bias of suitable value applied to its :25 control electrode or grid prevents the starting of an are between the cathode and anode but that once a current flow has started the bias on the grid has no further controlling efi'ect until the current has been reduced to zero.

In carrying the invention into effect the synchronizing impulses received from the transmitter are caused periodically to initiate the starting of a current through the discharge device which is of suificient energy to give the phonic wheel or the like the necessary driving force; the phonic wheel has means associated therewith for periodically interrupting the discharge through the device so making the current flow of the nature of impulses which are necessary for the driving of the phonic wheel and also enabling the control electrode to regain control of the discharge.

I may provide, in association with the phonic wheel, a rotary interrupter, the contacts of which are arranged to apply to the anode of the discharge device a transient negative voltage suitably phased with respect to the commencement of the passage of current applied to the phonic wheel through the discharge tube. The control electrode of the discharge tube may be normally biased to such a potential that the passage of an are through the discharge tube is prevented, and the incoming synchronizing impulses are then arranged to remove momentarily the bias on the control electrode so initiating the arc. The current passes to the phonic wheel giving it the necessary torque, and then the interrupter comes into play, stopping the are current, so allowing the control electrode to regain control ready for the next synchronizing impulse.

To enable the invention to be more readily understood, reference is directed to the following description of the accompanying drawing in which there is diagrammatically illustrated an arrangement embodying the invent-ion.

In the drawing I have shown an arrangement for use in connection with systems in which from a transmitter are sent out periodic impulses between which are periods in which no energy is transmitted, the periods of no energy transmission being utilized as synchronizing impulses. For utilizing the impulses for driving the phonic wheel 1 I have shown a gas-filled arc discharge device 2, having a cathode 3, a control electrode 4 and an anode 5 for controlling the transmis Connected in the anode circuit of the device 2 are the driving coils 7 and the anode of the device 2 is furthermore connected through a condenser 12 and a resistance 13 to the ositive terminal of the source 6. Associated with the phonic wheel 1 is a series of spaced contacts 14 arranged to rotate with the phonic wheel and to co-operate' with a stationary contact arm 15. The contacts 14 are all connected together and to a point on the anode circuit intermediate the connections between the condenser 12 and the resistance 13. The contact arm 15 is connected to the cathode 3 of the device 2. Contacts 14 are spaced to correspond with the teeth of the phonic wheel 1 and perform a purpose to be described hereinafter.

The operation of the arrangement is as follows:

A portion of the received impulses suitably amplified and of a unidirectional nature (this being ensured, if necessary, by providing a rectifier) is applied to the control electrode 4 of the discharge device through resistance 8,

the Voltage drop across which resistance, produced by the impulses, maintains the control electrode of the discharge device at a negative potential with respect to the cathode 3 sufficient to prevent the initiation of an are be tween the cathode and the anode 5. In the intervals between the impulses, i. e., periods of no currentreception, the voltage drop across the resistance 8 is temporarily remc .ed

and the control electrode 4 thereby attains the same potential as the cathode, thereby initiating an arc dischar 'e throughithe device. The

resulting current ow is applied through the driving coil 7 and causes the rotation of the phonic wheel 1. In order to stop the passage of current through the discharge device, it is necessary to apply to the anode 5 a transient negative potential suitably phased with respect to the positive discharge initiating potential applied to the control electrode 4. This is effected-by means of the contacts 14, co-operating with the contact arm 15 to connect periodically the anode 5 throu gh the condenser 12 to the cathode 3. The contacts 14 are so spaced as to apply the tra lsient negative potential to the anode 5 at a suitable interval after the current has commenced to flow through the device 2 and the driving coils 7. In the meantime, the control electrode of the discharge device has again been negatively biased by the received impulses so that the arc is thereafter prevented from starting again until the next period of no current reception, when it is once again initiated and the cycle above described repeated. The phonic wheel is thus rotated synchronously in accordance with the periods of no current reception and may thereby be caused to rotate in synchronism with a corresponding rotating element at the transmitter.

For phasing or isochronizing the rotating element at the receiver with that at the transmitter, the driving coils of the phonic wheel and the contact arm may be arranged to be rotatable as one unit about the axis of the wheel in the well-known manner.

This system is particularly useful in connection with television systems in which, for example, at the transmitting end any convenient scanning device with a rotating element may be employed which will, in general though not essentially, scan the object to be transmitted in a series of adjacent lines. It may be arranged in this device that by suitably constructing the scanning device, there is a short interval between the transmission of the end of one line and the commencement of the next, during which no light passes to the light sensitive device. In this short period either a special synchronizing signal may be sent outv or no signal at all. I may then use, at the receiver, either the normal picture signals, the space of no signals, or a special synchronizing" signal in this space as the means of initiating the are through the discharge device. Since the picture signals or synchronizing signals occur as regular pulses, the period or time between which is entirely dependent on the speed of rotation of the transmitting mechanism, it follows that the phonic wheel will rotate in synchronism with the transmitting mechanism.

Theenergy of the impulses passed through the discharge tube is thus dependent entirely upon its capacity, so that the phonic wheel may be of any power required provided a suitable discharge device is utilized, and is entirely independent of the energy of the synchronizing impulses or normal picture signals received; thus it is only necessary that the impulses should have suflicient value, either initially or after amplification, to produce or remove the bias on the control electrode of the discharge tube in order to initiate the passage of current therethrough.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. Apparatus for maintaining the rotation of a rotatable body in synchronism with received synchronizing impulses, comprising a phonic wheel for driving said body, a driving coil therefor, an electric arc discharge device provided with a control electrode for controlling the discharge between its cathode and anode for causing current impulses to be applied from a source of direct current to said driving coil, means for energizing said control electrode by said synchronizing impulses, means for maintaining the potential of the control electrode at a value such that no current can flow through the discharge device until the negative potential is removed by a synchronizing impulse, and means associated with the phonic Wheel for applying to said anode a periodic negative potential so phased with respect to the impulses applied to the control electrode that said control electrode regains control over the discharge in the time interval between successive synchronizing impulses applied thereto.

2. In a synchronizing system in which periodically interrupted signals are transmitted, the periods of interruption representing synchronizing impulses, apparatus for maintaining the rotation of a rotatable body in synchronism with received synchronizing impulses, comprising a plionic wheel for driving said body, a driving coil therefor, an electric arc discharge device provided with a control electrode for controlling the discharge between its cathode and anode for causing current impulses to be applied from a source of direct current to said driving coil, means for energizing said control electrode by said signals, means including an impedance in the circuit of said control electrode whereby said electrode is maintained at a negative potential by the voltage drop across said impedance caused by said signals, the circuit of said control electrode being such that the potential of the control electrode regains a value suflicient to initiate current flow through the discharge device during the pe riods of signal interruption, and means associated with said phonic wheel for applying to said anode a periodic negative potential so phased with respect to the impulses applied to the control electrode that said control electrode regains control over the discharge in the time interval between successive synchronizing impulses applied thereto.

3. Apparatus for maintaining the rotation of a rotatable body in synchronism with received synchronizing impulses comprising means for driving said body, an electric arc discharge device responsive to the received impulses for controlling the movement of said driving means and means associated with said driving means for supplying successive impulses to said device for rendering it inoperative.

4. Apparatus for maintaining the rotation of a rotatable body in synchronism with received synchronizing impulses comprising an impulse driven motor for rotating said body, an electric arc discharge device having an anode connected with said motor and a control electrode arranged to be actuated by the received signal, and means controlled by the movement of the motor for supplying successive negative impulses to said anode to cause interruptions in the discharge thereof.

5. Apparatus for maintaining the-rotation DiSOLAlMER I 1,874,774.Alan Julian Maddoclc, Wallserid-on-Tyne, England. ELECTRIC SYN- CHRONIZING SYSTEM. Patent dated August 30, 1932. Disclaimer filed August 4,1934, by the assignee, General Electric Company.

Hereby enters the following disclaimer to claim 3 of the said Letters Patent,

which is in the following Words, to Wit:

3. Apparatusfor maintaining the rotation of a rotatable body in synchronism I Withreceived synchronizing impulses'comprising means for driving said body, an

electric arc discharge device responsive to-the received impulses for controlling the movement of said driving means and means associated with said driving means for supplying successive impulses to said device for rendering it inoperative.

e [Oficial Gazette September 11, 1,934.] 

